It is believed according to the third generation partnership project (3GPP) that deployment of small cells and improvement in their abilities is one of the most interesting topics in the development of future communication networks. At present, one scene endorsed generally in the communication industry is that low power nodes are deployed within the coverage range or at the boundary of marco eNBs and compose collectively an access network in an evolved universal terrestrial radio access network (E-UTRAN) system, thereby providing joint data transmission services for user equipment (UE).
For such typical scene, reference is made to a system architecture shown in FIG. 1, herein an eNB which establishes an S1-MME interface with a mobility management entity (MME) in a core network (CN) and is regarded as a mobile anchor point by the CN is called a master eNB (MeNB); and an node which is connected with the MeNB through an X2 interface and provides extra radio resources for the UE is called a secondary eNB (SeNB). A wireless Uu interface is established between the UE and both the MeNB and the SeNB in order to transmit control plane signaling and user plane data, that is, the UE is in dual connectivity (DC). Since such system architecture enables two (or even more) eNBs to provide simultaneously the radio resources for one UE for communication services, data throughput of the network is improved greatly.
For user plane transmission and protocol stack form under such system architecture, reference is made to FIG. 2. Taking downlink data as an example, the transmission process is shown as in FIG. 2(a). A transmission operation of an EPS bearer #1 is the same as associated standards, that is, data packets are sent to the MeNB by a serving gateway (S-GW) through an S1-U interface, and then the MeNB sends the data packets to the UE through the Uu interface; and transmission of an EPS bearer #2 means that, after data packets are sent to the MeNB by the S-GW through an S1-U interface, only one part of the data packets of the bearer are sent to the UE by the MeNB through the Uu interface, and the other part of the data packets are delivered to the SeNB through an X2 interface and then are sent to the UE by the SeNB through the Uu interface.
A protocol stack form configurable by the EPS bearer #2 is shown in FIG. 2(b), i.e., the EPS bearer #2 has one packet data convergence protocol (PDCP) entity and two independent sets of radio link control (RLC) and lower level protocol entities. At a sending end of data, the PDCP entity located in the MeNB delivers one part of PDCP protocol data units (PDUs) to an RLC entity located in the SeNB for transmission, and the other part of the PDCP PDUs are sent by an RLC entity (and lower level protocol entities) of the MeNB itself. At a receiving end of the data, the two RLC entities process and then deliver the received RLC PDUs to the same PDCP entity to perform further operations, respectively.
Two scenes will exist in the process of data transmission and/or movement of the UE: one is, for example, that when variables in a certain protocol layer accumulate to a certain threshold, some configuration parameters of the UE are required to be modified; the other is, for example, that when signal quality decrease to a certain threshold, a serving eNB of the UE is required to be switched from the currently connected eNB (referred to as source eNB) to another appropriate eNB (referred to as target eNB). The two scenes need to be implemented through an intra-eNB change (the UE is connected with the same eNB both before and after the change, and only associated parameters are reconfigured) or inter-eNB change (the UE is connected with different eNBs before and after the change) procedure.
Under the system architecture described above, when the MeNB of the UE needs to be changed, according to the related techniques, the SeNB of the UE will be released before the change procedure or during the preparatory stage of the change procedure. If there are still nodes satisfying service requirements and appropriate conditions after the UE has access to the target eNB (for the intra-eNB change, the target eNB is the original MeNB), then the target eNB will add a SeNB to the UE. In an exemplary embodiment, for the intra-eNB change, if the condition of the original SeNB satisfies a threshold all the time, then both (intra-) change information of the MeNB and information on the release and re-adding of the SeNB may be carried by the MeNB in a piece of control plane signaling, i.e., only one piece of signaling is required to instruct the UE to reconfigure resources for the two eNB.
It can be seen that under the network related design ability, user plane data transmission between the UE and the SeNB will be interrupted because of the MeNB change for the UE. If the time it takes for the UE to have access to the target eNB cell is longer, then the time of the user plane data interruption between the UE and the SeNB will be lengthened accordingly. This means that radio resources that can be provided by the network for the UE are vacated, i.e., the data throughput of the UE which could have been increased is limited. Furthermore, overall performance of the network is decreased as well.